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Nanotechnology: Conducting DNA could mean improved biosensors
September 1, 2000

In many ways, DNA is almost the perfect building block for constructing tiny objects on the scale of nanometers (billionths of a meter). In some of the most promising research, scientists have recently learned to synthesize strands of DNA that conduct electricity. These “DNA wires” are made by plating the DNA with a thin coating of metal atoms. However, because the DNA serves only as a scaffold and is completely covered by metal, these wires do not retain all of the valuable properties of DNA, particularly its ability to bind selectively to other molecules. Now, researchers from the University of Saskatchewan have stumbled upon a discovery that could get around this shortcoming and greatly expand the use of DNA in a new generation of biosensors and semiconducting wires.

Researchers in the lab of biochemistry professor Jeremy Lee were investigating methods for stabilizing a novel form of DNA when they came upon a surprising result. They found that at high pH, or very basic conditions, DNA readily incorporates zinc, nickel and cobalt ions into the center of its helix. They knew this was the first step in making DNA conduct electricity. But unlike previous DNA wires, this new type of molecule, which they dubbed M-DNA, not only conducts but does so without losing its inherent ability to bind to other molecules.

The researchers are currently exploring applications that take advantage of M-DNA’s properties. One possibility lies in screening for genetic abnormalities. As with other DNA probes, the biosensor would work by binding a specially prepared sequence of DNA with the genetic sample to be tested. But in this case, the fully bound DNA strand is highly conductive; any deletions or mutations in the hybridized DNA act as a barrier that prevents electron flow. A computer can therefore spot these anomalies simply by measuring changes in conductivity.

The biosensor could also be used to identify compounds, such as environmental toxins, drugs or proteins, which bind to the M-DNA. “If we bind something to DNA, metal atoms are kicked out and interrupt the flow of electrons,” says Heinz-Bernhard Kraatz, University of Saskatchewan assistant professor of chemistry and a collaborator on the project. Because the reduction in signal strength is proportional to the concentration of the contaminant, the amount of environmental toxin can be readily determined. M-DNA could also be used to screen for new anti-tumor drugs that work by binding to DNA. “Biosensors are only the beginning,” says Kraatz. He notes that M-DNA could potentially be used in tiny semiconducting circuits in which the ” wires” will be the M-DNA molecules.

University Medical Discoveries, Inc., a Toronto-based technology development company, is providing funding for the project over the next two years. UMDI investment analyst Nick Glover anticipates the technology will be initially used to make a more sensitive DNA chip for genetic testing. “There are other DNA probes, but this one is potentially far more sensitive than other detection systems, and it’s also cheap and reusable,” says Glover. “The value of an enabling technology in this sector is likely to be significant.”

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